Spark plug



March 2.8, 1950 F. l. MccARTHY ETAL SPARK PLUG 2 Sheets-Sheet 1 FiledApril 6, 1945 BY@ f? uw? New?1 ATTORNEY March 28 1950 F. l. MCCARTHYETAL 2,501,826

SPARK PLUG Filed April 6, 1945 2 Sheets-Sheet 2 g' Y L'y' ff m . i zz Ez3 j; E i j@ J6' "l "i'f/ f S J7 .50 s 5f E /50 s 70 i; E 64, M y f y f4W 3,3 7g /35 1.9 55 ylegn f m 25 @2Q/ Zig. if.

9L 37d .3.3 613-- l 33 y sa K I A INVENTORS F/"f/zf/IMF 'Cd/y PatentedMar. 28, 1950 OFFICE SPARK PLUG Frederick I. McCarthy and CharlesSchandler,

New York, N. Y.

Application April 6, 1945, Serial No. 586,972

1 Claim. 1

This invention relates to spark plugs.

The object oi the invention is to provide a spark plug with quick andeflicient heat distribution. and leakage proof characteristics, and toprovide its parts in a manner which lend themselves particularly to massproduction.

The invention consists of a method in which a pre-shaped cartridge isformed by progressive pressures, which cartridge is then ready for insertion into a novel shell.

The invention consists in the combination of parts producing a novelresult, in which a sleeve with an extension to a sparking terminal isprovided with a direct heat transfer from the terminal to the body ofthe sleeve, and in which a spark gap extends beyond the end of the shellfor ready access `for cleaning, said shell having only one machinedbore; and in which said sleeve is pressure shrunk on the lining coveredspark terminal stem.

The invention consists in novel articles of manufacture, one consistingof the central sp-indle or stern having a spark plug tip in spacedVrelation to the inner cartridge having a pre shaped heat conductingmember which exerts a. leakage prooi pressure on the central stem; andthe other consisting ci a novel shell hav-- ing the usual exteriorhexagonal and screw threads, and having interior screw threads, asknown. but having only one machined bore, thus simplifying the structureand reducing the cost oi its making.

The invention will be more fully described hereinafter, embodimentsthereof shown in the drawings. and the invention will be pointed out inthe claim.

In the accompanying drawings,

l is a vertical central section of one embodirnent of the improved sparkplug, the parts shown being suicient to explain the invention, corelatedknown parts being omitted.

Fig. 2 is a vertical central. section of the improved preshapedcartridge, forming part of Fig. l..

Fig, 3 is a vertical central section oi the moldable member used in thecartridge shown in Fig. 2.

Fig. l is a vertical central section, partly in elevation ci theimproved shell,

Figs. 5, rfi and 'Y are diagrammatic plans of the circumferential boresof progressive dies used in pre-shaping the improved cartridge shown inFig.

Fig. 3 is a vertical central section of another embodiment of theinvention, showing a complete spark plug to the extent necessary toexplain the invention.

Fig. 9 is a vertical central section of the pre shaped cartridge used inthe spark plug shown in Fig. 8.

Fig. l0 is a vertical central section of the hard Wedge used to form thepre-shaped cartridge shown in Fig. 9, and

Fig. 11 is a vertical central .section of the softer and moldablematerial used in the cartridge shown in Fig. 9.

Similar characters of reference indicate corresponding parts throughoutthe various views.

Referring to the drawings, and more particularly to Figures 1 to 7, thecomplete spark plug in accordance to the invention consists of twoindependent parts, the outer shell lil, shown separately in Fig. 4, andthe pre-shaped cartridge 2li shown separately in Fig. 2. All that isnecessary in the assembly operation is to insert against frictionalpressure, the pre-shaped cartridge 20 into the shell I0, and then applya bringing home pressure P to the cartridge 2@ in order that itsexterior circumferential surface merges into the interiorcircumferential surface of the main bore of the shell, upon which thespark plug shown is ready for use, when assembled with its knownenvironmental parts, shown in our zio-pending application Serial No.559,880, filed October 23, 1944, issued to Patent No. 2,460,- 022 onJanuary 25, 1949, to which reference is herewith made.

The novel shell Ill is provided with the knowni hexagonal II, with itsinterior screw threads I2, circular rim I 3, and known exterior screwthreads I4. The main bore l5 is of subcaliber to the diameter oi theinterior threads I2, and a circular shoulder i6 is formed at thejuncture of these parts. The main bore l5 terminates near the bottom ofthe shell It at a shoulder Il, and that portion of the shell has acurved cutout I8 forming an air space I9 with the end of the cartridge20.

The pre-shaped cartridge 26 has the stem or spindle 2l provided with aspark plug tip 22 integrally therewith, and the stem is made ofstainless steel. Surrounding the stern 2| is a wrapped layer consistingof a plurality of sheets of mica forming a sleeve 23, which extendsalong the length of the stem, and seats on the inner surface 2li of thesparking tip This surface 24 is provided with a circular recess 25 intowhich a cylinder 2B of ceramic material is seated. Surrounding thesleeve covered stem 2| is a hollow cylinder 3D of soft moldable materialsuch This cylinder 3l) is shown separately in Figure 3. It has asubstantial length for extending along the stem. It has an exteriorcircumierential surface 3|, somewhat larger in diameter than thediameter of the main bore l5 oi the shell it. It has an interior bore 32oi the same diameter throughout, about the diameter of the externaldiameter of the mica sleeve 23. It has a constricted extension 33forming an exterior shoulder 34, and an internal bore 35 oi largerdiameter than the diameter of the bore 32. A curved portion 35 isprovided at one end of the bore 32 and a curved portion 3l at the otherend of the bore 32. To the extension 33 is secured by brazing orwelding, a circular disc 38 of nickel alloy, having an exterior andinterior diameter equal to those of the extension 33.

The mica sleeve 23 is wrapped around the stem 2 l in the manner wellknown. rhen the ceramic sleeve 26 is placed into the recess 25. Then thecylinder 33 is passed over the mica covered stem 2|, until the curvedshoulder Sla or the cylinder rests about on the ceramic sleeve 2li. A removable spacer 39 may also be used to space the as COppel.

terminal ring or disc 3.8 from the tip 22 to form the spark gap 40.

With the cartridge Darts just described assembled as described, the soformed cartridge is placed in a circular bore of a die having a diam*eter A, only the internal circumference 4| being shown in Figure 5, assuch dies are well known. The moldable cylinder 38 of copper issubjected to pressure and the distribution of this pressure exerts aconning effect upon the cylinder 30 radially inwardly and against themica sleeve 23. The object of the curved portions and 37 is to provide adiminution of pressure at these points, so as to prevent puncturing themica sleeve, all of the pressure applied radially inwards against theremaining portion of the mica sleeve being substantially equal and thusnot likely to puncture the sleeve.

The cartridge is then removed from die 4 I, and placed in a die 42,Figure 6, which has a slightly smaller internal diameter B and pressureis again applied, all as described in connection with Figu're 5; and allthis is repeated with die 43 of Figure '7, which has its diameter Cagain slightly smaller.

Thus, the external diameter of the cylinder` 3U ,.o

becomes progressively smaller.

The respective pressures are about 2000 pounds each and these successiveand progressively smaller diameter pressures shape the cartridge intosemi-final shape, such as to justify the appelation of a predormed orpre-shaped cartridge. Such a cartridge is shown in Figure 2, and isready to insert into the shell I0 of Figure 4, after which insertion, aiinal pressure P is applied and the spark plug of Figure 1 results.

The method described includes subjecting a moldable cylinder to radiallyinwards pressures against a central sleeve of mica to secure it inleakage proof condition or seal against the spari'- ing tip stem underprogressively smaller diameters, and then subjecting the cylinder ofmoldable material to a pressure distributed radially outwards againstthe bore of the shell to provide a leakage proof seal therebetween, andobtain a. heat transfer action between the cylinder and shell, due tothe absence of air between these parts.

The surface 38a of the nickel sparking terminal 38 extends slightlybeyond a plane passing through the surface Illa of the shell I0, andconsequently the spark gap 40 is beyond the end of the shell I0, andthus may be readily cleaned by simple means and without taking the partsof the plug apart. At the same time the space I9 serves the function ofan air chamber in close proximity to the spark gap 40. The nickel disc38 and the extension 33 of the cylinder 30 are arranged in the mannerdescribed to provide a. direct path of heat flow from the spark gap tothe body of the cylinder 35|. from which the heat is transmitteddirectly to the shell.

The method described and the combination of the cylinder extension withits nickel disc extending slightly beyond the end of the shell for readyaccess for cleaning, combined with the direct heat transmission by aunitary structure, may be applied to a spark plug made by the use of awedge 5| of beryllium copper, a metal or alloy much harder than thesofter moldable sleeve 5U, as shown in Figures 8 to l1.

Reference is here made to our copending application Serial No. 584,800,led March 26, 1945, issued to Patent No. 2,471,070 on May 24, 1949, andthe method therein described may be used, by forcing in the berylliumcopper sleeve 5| from its draft initial position to its final position,and the novel combination of the extended sparking gap and direct heattransmission availed of or, the method described in connection with theprogressively smaller dies may be used.

The beryllium copper sleeve 5| is shown separately in Figure 10, and hasan external diameter slightly larger than its external diameter whenfinally in use, as in Figure 8, that is after the radially inwardpressures of the progressive dies have been applied. The exteriorsurface 53 is cylindrical and about the circumference of the main boreof the shell (Fig. 10) but its outer diamter is larger than the innerbore diameter. The inner bore 54 of the sleeve 5| is frustoconical, withthe apex 55 of the cone forming a larger base portion 56 of the wedge,than the apex end 51 of the wedge 53. The contacting surfaces may becylindrical.

O1', the moldable sleeve 50 is also largely of Vfrusto-conical shapewith its exterior surface 58 inclined at an angle of about 2, which inclination is that of the inner bore 54. The outer sleeve 5| may beeither in draft to the inner sleeve 5|) and the parts brought home, orthe inner surfaces can be co-extensive initially as in Fig. 9. Inaccordance with the present invention, in either case, the outerdiameter of the sleeve 5| is larger than the main bore |5 diameter, andthe cartridge is subjected to the successive and progressive pressuresof the dies 4|, 42 and 43, to bring the outer diameter of the sleeve 5|to equal that of the bore |5, after which insertion of the cartridgeinto the shell takes place and the pressure P is applied to thecartridge in order to distribute it to the peripheral surface of thesleeve 5i and merge it into the bore 5 surface to obtain a leakage prooflit and a good heat transfer contact. The length of the exteriorinclined portion 58 is equal t0 that of the inner bore 54 of the sleeve5|. The inner bore 59 of the sleeve 50 extends beyond the length of theexterior portion 58, and terminates at one end in a curved enlargement36 and at the other end in a similar curved enlargement 31; theenlargement 31 forming a shoulder 37a at the end of a, bore 63 of largerdiameter than the bore 59. An external shoulder 64 is provided having anexternal diameter substantially that of the main bore of the shell Il).l

A nickel disc is applied to the end oi the sleeve 50. Thus, from theparte; described the sleeve 50 has an extension which acts a directtransmitter of heat.

The new result obtained is the accessibility of the spark gap forcleaning; and the direct trans mittal of heat, by the arrangement of theparts described as part of the spark plugs shown in Figures 1 and 8.

The novel method is the subjection of the mold able member tcprogressive radially inward pres sures to assure the compacting of themica layers against the stem and against each other to secure a leakageproof seal, and the subjection of the cartridge to pressure appliedvertically and trans mitted and distributed radially outwards to ob1utain a leakage prooi air seal and intimate molecular contact for heattransmission between the cartridge and the shell.

The novel shell requires only the machining necessary for its main bore,and the novel cartridge differs from a cartridge having a draft likethat shown in our Patent No. 2,460,022 in that the cartridge ispre-shaped to almost final condition before its entrance into the boreof the shell. Thus the simple shell and the pre-shaped cartridge providea most simple manner of assemblage capable of utilizing relativelyunskilled labor.

The tip 22 is of stainless steel, the ring 38 of nickel and the ring isof some depth for wear and tear; the inner sleeve 50 is of softer copperthan the harder copper of the sleeve 5| using in the preferred form anadmixture of beryllium; the sleeve 30 is of copper which is moldable orcompressible under the radially inwards pressure applied, and preferablyis such as not to flow too easily and beyond the surface I6 of theshell, and we have obtained good results by using a beryllium coppersleeve 30, which while hard has still its modulus of elasticity orcompressibility under the pressures applied radially inwards. Carbonsteel is used for the shell I0.

When the successive and progressive radially inward pressure method isused, all the compression work is done on the cartridge outside of theshell, and thus the shell is safeguarded against the possibility ofspringing open, or from being subjected to excessive strains andstresses, which may affect its heat conductivity or its inherentresiliency.

Spark plugs made under the disclosure of our Patent No. 2,471,070 havegiven excellent ratings of over 400 and passed the endurance tests; andit is believed that spark plugs made in accordance with this disclosurewill be of higher rating and also present improvements in production andassembly.

Spark terminals extending outside of the shell are known, but theimprovement of this part of the spark plug is to extend the parallelsurface spark gap outside of the shell enabling a cleaning tool to beinserted between the parallel surfaces of the kind disclosed in U. S.Letters Patent No. 2 357,602 of September 5, 1944 to Melville F. Petersand Fred I. McCarthy.

It will be noted that the spark gap terminal is made a part of thesleeve extension 33, this having heretofore been part of the shell; andthus a much quicker heat transfer takes place. It will also be notedthat the moldable sleeve action is direct on the covered stem, withoutany intermediate parts. The stem may be provided with a silver or partsilver core to increase the heat conductivity of the stem and dissipatethe heat of the sparking tip,

The improved spark plug is specially intended for high altitude flights(30,000 feet) where the motor gets hot and thus the sparking terminalsexpand and somewhat reduce the gap which is advantageous. The ring 38 isresponsive to the extension 33 expansion, and the tip 22 to the tip andstem expansion.

When the cartridge is about to be inserted in the shell the pressure Pis applied to the cartridge which pressure is about 5000 pds. to bringhome the cartridge in the shell.

The initial diameter is reduced about .004 with each radial compression.

In the nished spark plug, the spaces formed by the rounded portions 36and 31, are filled with cement, in the known manner.

We have described several forms of our invention., but obviously variouschanges may be made in the details disclosed without departing from thespirit of the invention as set out in the following claim:

We claim:

En a spark plug having a central stem one end of which forms a sparktip, an insulating layer around the main portion ci said stem, acompression member surrounding the insulating layer having a flatsurface forming a spark tip, and having a circumferential cylindricalcutout with a curved surface at its inner end, and a shell enclosing thecompression member and in electrical connection therewith, said sparktips extending outside of the shell, the combination of a circularshoulder on the spark tip end of the stem abutting against an end of theinsulating layer, a circular groove in said spark tip end exterior tosaid shoulder, a iiat surface circumferentially and radially disposedaround said circular groove and parallel with said flat surface of thecompression member, and spaced therefrom to form a spark gap, and aporcelain cylinder seated at one end in the circular groove andhuggingly surrounding the end portion of the insulating member on theshoulder, and forming the inner wall of the spark gap, the other end ofthe porcelain cylinder being in said cut out and seated against itscurved surface.

FREDERICK I. McCAR'II-IY. CHARLES SCHANDLER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,126.975 Furber Feb. 2, 19151.556,251 Sampson Oct. 6, 1925 1,968,314 1Rohde July 31, 1934 2,064,089Stemmeler Dec. 15, 1936 2,083,916 Mascuch et al June 15, 1937 2,225,105Flynt Dec. 17, 1940 2,296,033 Heller Sept. 15, 1942 2,357,602 Peters etal. Sept. 5, 1944 2,360.287 Smith Oct. 10, 1944 2.376,362 Kasarjian May22, 1945 2,391,458 Hensel Dec. 25, 1945 FOREIGN PATENTS Number CountryDate 25,582 Great Britain 1897

